Photonics Research, Volume. 13, Issue 7, 1991(2025)

Spiral resonator referenced low noise microwave generation via integrated optical frequency division

Long Cheng1、†, Mengdi Zhao1、†, Yang He1、†, Yu Zhang2, Roy Meade2, Kerry Vahala3, Mian Zhang2, and Jiang Li1、*
Author Affiliations
  • 1hQphotonics Inc, Pasadena, California 91107, USA
  • 2HyperLight Corporation, Cambridge, Massachusetts 02138, USA
  • 3T. J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, California 91125, USA
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    Figures & Tables(5)
    (a) Spiral resonator referenced on-chip low noise microwave generation architecture based on integrated optical frequency division. The lasers are locked to two cavity modes of an ultra-high-Q spiral resonator. Due to common mode noise cancellation of the co-locked lasers from a single resonator, their frequency difference (ν2−ν1) achieves low frequency noise below the cavity thermal noise limit. By anchoring the spectral end points of an integrated electro-optic (EO) comb to the dual laser reference, the fractional stability of the dual laser reference (ν2−ν1) is transferred to the EO comb line spacing (microwave rate). And the phase noise of the EO comb line spacing is divided down from the phase noise of the dual laser reference. (b) Photograph of the 14-m-long Si3N4 spiral resonator. (c) Image of the tandem thin-film LiNbO3 phase modulator (PM) including two PMs on the same chip. The middle section is not shown.
    (a) Beat note phase noise of co-PDH locked lasers (blue) and free-running lasers (red). Relative phase noise of the co-PDH locked laser to the spiral resonator is reduced below the cavity TRN noise limit (which is shown as the green curve). (b) Comparison of on-chip low noise dual laser references. The current work has achieved record low on-chip relative laser phase noise from 10 Hz to 10 kHz offset. (i) Two lasers co-self-injection-locked to a Si3N4 spiral resonator [18], (ii) dual Brillouin lasers from a silica disk resonator [31], (iii) dual Brillouin lasers from a Si3N4 ring resonator [32], (iv) two lasers co-PDH locked to a 4 m Si3N4 coil resonator [15], (v) OPO signal and idler from a Si3N4 ring resonator [17], (vi) this work.
    (a) Broadband integrated EO comb spectrum with 3 dB bandwidth of 4.4 THz is generated from the tandem TFLN PM chip. (b) Optical spectra of the co-PDH locked lasers spanning 27 nm (red), and the TFLN EO comb (blue) under eOFD operation. Inset shows the zoom-in EO comb lines at the spectral middle point between the two lasers.
    (a) Schematic of the experimental setup for the chip-based PMO. (b) Microwave phase noise of the chip-based PMO at 37.3 GHz carrier (blue). The dashed green curve is the phase noise of the 10 GHz carrier scaled from the 37.3 GHz PMO output. Yellow curve is the phase noise of the co-PDH locked lasers. Brown curve is the phase noise of the free running VCO at 37.3 GHz. Dashed black curve is the projected PMO phase noise by scaling down the co-PDH locked laser phase noise by 39 dB. Insets are the RF spectra for the PMO in locked (RBW 2 Hz) and free-running cases (RBW 1 kHz).
    Residual PDH locking phase noise is plotted (black curve) for one of the external cavity diode lasers (RIO laser) when it is locked to the 14 m Si3N4 spiral resonator. Blue curve is the co-PDH stabilized dual laser phase noise.
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    Long Cheng, Mengdi Zhao, Yang He, Yu Zhang, Roy Meade, Kerry Vahala, Mian Zhang, Jiang Li, "Spiral resonator referenced low noise microwave generation via integrated optical frequency division," Photonics Res. 13, 1991 (2025)

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    Paper Information

    Category: Integrated Optics

    Received: Mar. 20, 2025

    Accepted: Apr. 29, 2025

    Published Online: Jul. 2, 2025

    The Author Email: Jiang Li (jiang.li@hqphotonics.net)

    DOI:10.1364/PRJ.562434

    CSTR:32188.14.PRJ.562434

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